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Recently there have been few projects, so I have some time to read and share something with everyone: (Teacher Li Shiyu’s \"Training Manual for Pressure Vessel Design Engineers\”). Notes on the thickness of steel materials after welding heat treatment: The thickness of this steel refers to the thickness specified in the material quality certificate, that is, the thickness indicated on the completion drawings of the vessel. Since in our country, the design and manufacturing of most pressure vessels are carried out by different entities, and due to factors such as process thinning during manufacturing, it is common to add a margin to the nominal thickness specified in the design drawings when purchasing steel. For a vessel made of 16MnR with a nominal thickness of 28 mm, it would seem that no post-weld heat treatment is necessary based solely on the nominal thickness; however, factors such as process-induced thinning may lead to the use of steel with a thickness of 32 mm, which exceeds the threshold requiring post-weld heat treatment. To resolve the aforementioned contradiction, the standard specifies that the actual thickness, rather than the nominal thickness, is used as the basis for determining whether post-weld heat treatment is required. It can be seen that when the nominal thickness approaches the critical threshold value for post-weld heat treatment specified by standards, designers should pay special attention to selecting a solution that offers both safety and cost efficiency.